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Membrane filtration can be accomplished with either dead end filtration or crossflow filtration. Dead-end: Filter cake can form reducing filtration capacity. Crossflow: Maintains more steady permeate flux and low pressure. TWO MAIN TYPES OF FILTRATION Figure: Created by Group 7 4

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Employs tightest membranes for liquid separation. Only allows small water-soluble ions to go through membrane along with water. REVERSE OSMOSIS 6

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Removes multivalent ions and small molecules in nanometer range like sulfate ions, and sugars. The most common type used for nanofiltration is the spiral membrane. NANOFILTRATION webdoc/webb8uefdg of-water/water-filtration/membrane- filtration/nano-filtration 7

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Used to retain relatively large dissolved materials like proteins and starches. Ultrafiltration membranes are typically classified by their ability to retain component specific sizes. ULTRAFILTRATION c/reverse-osmosis 8

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Suspended solids and large colloids are rejected, while dissolved solids and macromolecules pass through Operate at low pressures of 10 psi or less. MICROFILTRATION 9

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Membranes are fabricated from variety of materials Made of Inorganic and organic materials Metals, polymers, and ceramics are used for different applications based on their properties FABRICATION OF MEMBRANES 11

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Polymers are utilized most because of their price and versatility Polymer membranes are typically made up of a thin layer of polymer on a porous backing, creating a material with high permeability, selectivity, mechanical strength, and chemical stability POLYMERS 13

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Very few commercially available membranes are symmetric throughout their thickness Some examples include: Polytetrafluoroethylene Polyethylene Polypropylene SYMMETRIC MEMBRANES pansion 16

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Include most of the commercially available membranes Have either a thin microporous or dense permselective layer supported by a more-open porous substrate The membrane may by integrally skinned, formed in a single operation, or by separate steps An example of an asymmetric membrane is cellulose RO membrane, where both layers are made up of cellulose acetate. ASYMMETRIC MEMBRANES nanotechnology/nanofiltration-separations-part-1- nanotechnology/ 17

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A composite membrane is a subset of asymmetric membranes The skin layer and support layer are made up of different polymers based on the individual properties The skin layer determines separation performance Support layer determines mechanical stability An example of a composite membrane is a polymide RO membrane which is made up of a thin polyamide permselective skin on a polysulfone UF support. COMPOSITE MEMBRANES 94/issue-48/in-this- issue/production/membranes-solve-north-sea- waterflood-sulfate-problems.html 18

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Cassette membranes are used for UF and MF. The membrane filtrates the fluid, while the gaskets are used to separate the permeate, feed, and retentate streams. Spacers introduce turbulence, which increases mixing and prevents the formation of a gel layer. However, spacers are sometimes prone to particulate clogging, and can be difficult to clean. CASSETTE Source: "Understand the Basics of Membrane Filtration." Wang, Hua. Hongyi, Zhou. GE Global Research. 20

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Utilizes laminar flow for MF, UF, or NF. Composed of a large number of hollow-fiber membranes in a cylindrical housing with permeate ports and end caps. Has a very high packing density, therefore has a high surface area to volume ratio, making this particular filter ideal for product recovery. CARTRIDGE Source: "Understand the Basics of Membrane Filtration." Wang, Hua. Hongyi, Zhou. GE Global Research. Source: amazon.com/images/I/41za yl%2BuLzL._SY300_.jpg 22

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Spiral Wound are used predominantly for RO. They are composed of a multi- layered assemble of flat sheet membranes, and spacer screens. These components are all rolled around a perforated tube, which seals the membrane and spacer layers on three sides. SPIRAL WOUND Source: "Understand the Basics of Membrane Filtration." Wang, Hua. Hongyi, Zhou. GE Global Research. 23

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They are built to have a high packing density by utilizing thin spacer screens. Industrially, large-scale operations use these RO modules connected in parallel with one another. SPIRAL WOUND MODULE USED FOR RO Source: /Reverse_osmosis_membrane_coil.jpg 24

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Membrane filtration has lots of applications! Several types of driving forces for membrane filtration: Pressure Difference Concentration Difference Temperature Difference Used in many industrial processes: Desalination Wastewater and process water treatment Biopharmaceutical applications CONCLUSION Different types of membranes can be applied to various applications based on particle size: Reverse Osmosis (Smallest constituent) Nanofiltration Ultrafiltration Microfiltration (Largest constituent) 37

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Add a chemical to the solution being filtered to make membrane more durable Combine multiple driving forces Introduce turbulent flow to prevent clotting SUGGESTED WORK FOR IMPROVEMENTS tabid/115/language/en-GB/Default.aspx 38